Treatment of pulverulent materials



Mach I8, 1969 M. BOUCRAUT ETAL 3,433,624

TREATMENT OF PULVERULENT MATERIALS Original Filed May 18, 1965 UnitedStates Patent 99,050 US. Cl. 75--1 Int. Cl. C22b 1/10; C21b ]/02 9Claims ABSTRACT OF THE DISCLOSURE Pulverulent materials are fluidizedand subjected to heat treatment by passing the material in an even flowalong a predetermined path through an enclosed space forming a singlefluidizing bed while introducing the treating gases int-o the enclosedspace at a plurality of sets of inlets spaced along said path, the gasesemanating from said sets of inlets having from set to set differingphysical and chemical characteristics.

An example is the roasting and fluidizing of iron ore wherein thepreheated ore is passed along the path forming the fiuidizing bed and aneutral gas is supplied to the first stage, an oxidizing gas is suppliedat a second stage and a relatively slightly reducing gas is supplied ata third stage and a relatively strongly reducing gas is supplied at afourth stage of the travel of the ore along said path. Each stage maycomprise a plurality of inlets for a combustion gas obtained from a fueland varying amounts of preheated air.

This application is a continuation of application Ser. No. 456,689,filed'May 18, 1965, now abandoned.

The present invention relates to a process for treatment of pulverulentmaterials and, more particularly, to a process wherein fluidization ofthese materials is effected by gas currents.

It is an object of the present invention to improve treatment ofpulverulent materials in the presence of gas and, more particularly, toimprove the heat balance of such treatment.

A more specific object resides in a fluidization process which permitsthe elimination of parasitic components such as water, both in itsmolecular form and in the form of hydrates, and carbon dioxide.

A still more specific object of the invention is to provide means inconnection with a fluidization process either for dehydration with thehelp of a neutral gas and at comparatively low temperatures or fordecarbonation with the help of an oxidizing gas at a much highertemperature.

Under a more general aspect, the invention is directed to a fluidizationprocess which permits an effective control of a cycle of thermalconditions and of a cycle of specific gaseous atmospheres in order toobtain a very high yield and thus an improved heat balance.

These and other objects, as they will appear from the followingdescription, are accomplished broadly by fluidizing pulverulentmaterials in one and the same bed formed in an enclosed space by meansof a plurality of gas currents in which the different gases havedifferent physical and chemical characteristics.

Specific features of the invention are the following:

(a) At least one of the gases of a given composition is introduced intothe enclosed reaction space by a plurality of different inlets.

(b) The gas, or the several gases, are obtained by a 3,433,624 PatentedMar. 18, 1969 combination of a combustion supporting agent and acombustible material.

(c) The introduction of the several gases into said enclosed space isindividually controlled.

(d) The different gases have different temperatures.

The process of the invention is of particular significance for thosepulverulent materials for which the chemical composition and thetemperature of the fluidization gas plays an important part. Thus, ifthere are employed oxidation reactions followed by reduction reactions,the compositions and temperatures of the fluidization gases arecritical.

As already pointed out, the process of the invention permits to get ridof waste materials, such as water and carbon dioxide, and also enablesboth dehydration and decarbonation, depending on whether a neutral gasand a lower temperature or an oxidizing gas and a higher temperature areused. Neutral gas in this connection means a gas which has neither anoxidizing nor a reducing effect in respect of the particular pulverulentfluidized material.

The following is a more specific example of the invention which,however, should not be understood as a limitation in any manner of thegeneral concept disclosed. The example will be described with referenceto the attached drawings, in which:

FIG. 1 is a diagrammatic showing of a reactor for a magnetic roastingprocess as employed in the present invention;

FIG. 2 is a plan view, also in diagrammatical form, of the reactor shownin FIG. 1 along lines ab, and

FIG. 3 represents a vertical section in diagrammatic manner along linesc-d.

The reference number 1 generally refers to a reactor for the magneticroasting of French Lorraine-type iron ore which is introduced inpulverulent form into the reactor through conduits 2, 2a and 2b. The orewhich has previously been heated in an apparatus, not shown, to 250 C.is fluidized through the combustion gases which emanate from the slots 3of three burners 4, 4a and 4b. The burners are fed in conventionalmanner with preheated air and heavy fuel by conduits such as indicatedat 5. The combustion in burners 4, 4a and 4b takes place instoichiometric proportions and in a manner that the gases which fluidizethe ore at its entry into the reactor are neutral, that is, neitheroxidizing nor reducing.

While the introduction of fresh ore through conduits 2, 2a and 2bcontinues, the ore which has been subject to fluidization by the gasesof the burners 4, 4a and 4b is progressively moved on to a place aboveand around the burners 6, 6a and 6b which are also fed in conven tionalmanner with preheated air and heavy fuel through conduits indicated at7. The combustion in burners 6, 6a and 6b takes place with an excess ofair so that the gases which flow out of slots 3a are oxidizing gases.

The movement of the ore particles in the bed continues, and theparticles thus reach the zone of burners 8, 8a and 8b, which again arefed in conventional manner with preheated air and heavy fuel throughconduits as shown at 9. The combustion in burners 8, 8a and 8b takesplace with a slight deficit of air so that the combustion is incompleteand the combustion gas entering through slot 3b is of a reducing nature.

The particles finally arrive at the area of burners 10, 10a and 10b,which are likewise supplied with preheated air and heavy fuel throughconduits 11, 11a and 11b. The combustion in these burners is effectedwith a substantial deficiency of air, so that the gases originating fromburners 10, 10a and 10b through slots 30 are strong reducing agentswithout, however, causing carbon black particles to form.

The treated ore is removed from the single fluidization bed 12 throughconduits .13, 13a and 13b, and is led to an exchanger of conventionaltype wherein it will give off a substantial portion of its sensibleheat, which heat then is used to preheat the fresh ore entering throughconduit 2 to a temperature of 250 C. The gases are blown out throughconduits 14, 14a and 14b, which have their inner inlets in the upperportion 15 of the enclosed space 1, which portion may be designated -asthe return level.

The following examples illustrate the application of the inventionwithout any intention of limitation. Thirty tons per hour of crude anddry Lorraine-type ore of the composition shown in Table I were treated 4The outflow of gas in this zone was 2025 Nmfi/h. or

2025 =3880 mfi/h. or 1.077 mfi/sec.

assuming that atmospheric pressure prevailed in the enclosed space. Thevelocity of the gas when there were no particles in the fluidization bedwas 1.08 m./sec.

This velocity is sufficiently weak to avoid the entrainment of theparticles. However, after the ore has been treated by the gas, the gaswas then blown towards the upper portion of the reactor, the so-calledreturn level where it no longer contained fluidized particles.

(2) A heat balance was established also for each of TABLE I MineralCorn- Weight, Contents of Individual Components poneuts percent 6 $10208.0 A1203 CO2 H20 FZH' In order to establish an overall heat balanceheat balances were set up for the individual stages. On the basis thatthe reactor 1 occupied a space of 12 m? (3 x 4 m.) and that each burnerserved a portion of the fluidization bed having a cross-sectional areaabove the burner of 1 m. individual heat balances for the differentstages were established as follows:

(1) In the zone of burners 4, 4a and 4b the fluidization gasesoriginating from the burners were neutral. Their function was todehydrate the ore, that is, to remove therefrom molecules of constituentwater as distinguished from the accidental humidity which had alreadybeen eliminated during the preheating of the ore.

The gases which originate from each burner on this level accordinglymust dehydrate t./3=10 t./hour of ore, that is, 830 kg./h. of water or1030 NmF/h. of Water vapor which corresponds to a thermic requirement of740 therms/h. (one therm, abbreviated th., equalling one million smallcalories and mth. standing for millither-m). For this purpose there wereused up 80 kg./h. of heavy fuel which was preheated at 250 C. andcombined with air, the latter being preheated to 300 C. The gas balanceof each of the burners 4, 4a and 4b was, therefore, as shown in thefollowing Table II.

TABLE II Combustion gases from 80 k /h fuel g. 140 112 740 992Dehydration l, 033 1, 033

Total in Nmfi/h 140 1. 145 740 2, 025

burners 6, 6a and 6b. The gases originating from each of the burners inthis zone were oxidizing gases, which permits to raise the heat level ofthe particles on an average to 525 C., which is the temperature requiredto decompose the carbonates and, in particular, the siderite. Theoxidizing gases also converted all iron oxides into sesquioxide (Fe OThe chemical and mineralogical composition indicates that there were 160kg./h. of CO attached to the iron of the siderite per ten tons of oretreated each hour. By decarbonization at about 500 C. this wasequivalent to a weight loss of 160 kg./h., that is, an input of 80 Nm./h. of CO in the gas. This composition also indicated that the sideritein its crystalline network contained a very small portion of CaCO(Ca0=0.2), which was closely attached to the FeCO and which was alsodecomposed around 500 C.

The decomposition reactions accordingly are the following:

The endothermic reactions resulted therefore in the following heatrequirements:

150 kg./h. 56

20 kg./h.

X 42.5 th./h.

The oxidation of all ferrous iron to the Fe O stage proceeded accordingto the following exothermic reaction:

ZFCO /2 O2" mth.

TABLE III Input and Inflow Requirements and Outflow Combustion of kg./h.fuel 800 th./h. Dehydration 740 th./h Available heat of 10 t./h. oreintroduced at 250 0.: Available heat of the ore: 9.17X0.2 (25026) 413th./h

10X0.2 (250-25) 450 th./h. Available heat of the gases: Available heatof the air preheated to 300 0.:

-- CO2 H2O N 2 02 N; N 3 m. 1.145 740 NmJ/h 196 Mth./ I Im. 100.40 82.44 70. 31 th./h. MthJNm. 89.66 86 38 82 th./h. Losses and sundry 19th./h.

1,832 th./h. 1,332 thJh.

Nm. /h. was necessary. This oxidation reaction thus leads to a thermicinput of GO: in 1110 in N; in Total in Nmfi/h. Nmfi/h. Nmfi/h. Nmfi/h.Combustion gases from 30 kgJh. of fuel 52 42 280 374 N: derived fromexcess oi air 260 260 C0, of decarbonation 80 80 Total in NmJ/h 132 42540 714 The heat balance in the zone of each of the burners 6, 6a and 6bwas therefore as shown in Table V, assuming that the average temperatureof the bed in this zone was Nm. /h.

CO 34 CO 70 H O 28 H 56 N 315 Total 503 that is, 126 Nmfi/h. of CO+Hwere available for partial reduction.

The complete combustion of 60 kg./h. of heavy preheated fuel oil wouldhave resulted in a thermic input of 600 th./h. Since the combustion,however, was incomplete, there could be deducted the deficiency intherms caused by the presence in the gas of 70 Nm. of CO and 56 Nm. ofhydrogen. On the basis of these amounts the following theoreticalreactions, however, did not materialize The partial combustion of 60kg./h. of fuel oil instead supplied only 525 C., and that the specificheat of the ore was 0.21/ 70 56 6 0 mthjkgjo C, 0 th 67 6 57 7x 244.5th./h

TABLE V Input and Inflow Requirements and Outflow Combustion of 30kg.[h. fuel 300 thJh. Available heat of the ore: 9.11X0.21X(52525) 957th./h. Decarbonation and oxidation 355 th./h. Available heat of thegases: Available heat of the ore 413 th./h. Available heat of the airpreheated to 300 0.: 1110 N1 Oz N1 N H-Ill 42 540 MthJNm. 191.38 159.92127 th./h. Nmfi/h 143 540 MthJNm. 89.66 86. 38-) 59 thJh. Losses andsundry 43 thJh. 1,127 tIL/h. 1,127 th./h.

The velocity of the gases when there were no particles in this part ofthe bed was 525+273 1 1 714 X 273 3600 sec. X 1 m? ,vhich velocity wasentirely adequate to maintain the particles in fiuidization.

=0.58 m./sec.

(3) Regarding the heat balance applying to the zone 45 of each ofburners 8, 8a and 8b it is noted that in this part of the bed eachburner operated in a reducing atmosphere so as to assure the partialreduction of the ore to magnetite. The reduction reactions are asfollows:

Oxidation of 126 Nm. /h. of CO+H by part of the 0 oxygen bonded to theiron amounted to a weight loss 0 the following Table VI, if thetemperature in the bed was 600 C., and the specific heat of the ore at600 to 650 C. had the value of 0.22 mth./kg/ C.

TABLE VI Input and Inflow Requirements and Outflow Incomplete combustionof kg./h. fuel 244 thJh. Available heat of the ore:(9.11-0.09)X0.22X(60025) 1, 141 th./l1. Heat of reaction 33 th./h.Available heat of the gases: Available heat of the ore 957 th./h.Available heat of the preheated air: 001 H1O N1 0: N2 Nmt lh 104 84 315Mill/N111. 285. 222.68 185.85 107 th./h. Nmfi/h 83 315 Losses and sundry21 th./h. Mth.lNm. 89. 66 86.38 35 th.lh. l, 269 th./h.

1,269 thin.

The reduction of Fe O therefore required an amount of 22,400/56 6=67liters of reducing gas (CO or H per kg. of iron, that is, 673470=232,000 l. or 232 Nrn. /h. of CO+H for 10 t./h. of ore. The amountof fuel oil consumed in each of the burners 8, 8a and 8b was 60 kg./h.The gases originating from each burner at 800 C. had the followingcomposition:

The total outflow of gas in this zone of the bed was 503 Nm. /h. at 600C., that is, a velocity in vacuo of (4) In respect of the heat balancein the zone of each of the burners 10, 10a and 10b the followingapplies.

The gases originating from each of the burners 10, 10a and 10b shouldassure the complete reduction of the ore to magnetite. The gases,therefore, must be strong reducing agents in order that the gasesflowing out of the fluidi zation bed, after reduction of the Fe Oremaining in the amount to any limitation since equivalent means formagnetite, still contain 4 to 5% of CO+H at the return carrying out theinvention may be employed without delevel. Their temperature reached 800C. at the burner parting from the scope thereof. We therefore do notwish outlets. A portion of their available heat however, was to belimited otherwise than by the language of the passed on to the ore sothat at the exit of the fiuidization 5 appended claims. bed the gastemperature was down to 650 to 700 C. What is claimed as new and desiredto be secured by As stated, in the preceding zone there were producedLetters Patent is: 126 Nm. /h. of reducing gas as against therequired 1. The process of treating pulverulent material adapted 232 Nm./h. It was therefore necessary to provide for to be oxidized andreduced, comprising passing the maan input of 106 Nm. /h. of CO+H inorder to reduce terial in an even flow along a predetermined substanallof the sesquioxide of iron to magnetite. The removal tially horizontalpath through an enclosed space forming of oxygen resulted in a weightreduction of the ore a single fluidizing bed; introducing combustiongases into amounting to the enclosed space at a plurality of sets ofinlets spaced 16 kgxmfi along said path, the combustion gases emanatingfrom =76 kg./h. the sets of inlets having from set to set differingtemperatures and oxidation-reduction rates with respect to their Usingfuel oil in the amount of 60 kg./h. the gas balance ff n i pulverulentmaterial; n removing h in the zone pertaining to each of the burners 10,10a and thus-treated pulverulent material at the end of said path. 10bappears from the following Table VII. 2. The process of claim 1, whereinsaid sets of inlets TABLE VII CO1 in CO in H2O in H1111 N2 in Total inNmfi/h. Nmfi/h. Nmfi/h. Nmfi/h. Nmfi/h. Nmfi/h.

Gases at burner outlet at the temperature of 800 O 34 70 28 56 315 503Gases at outlet of the fluidlzation bed at 650-700 C"... 94 10 74 10 315503 As appears, the gases at the exit of the fiuidization bed, include afirst set in the direction of said flow and wherethat is, at the entryto the return level, still contain 4% in the combustion gases suppliedthrough said first set of reducing gas (CO+H which is in accord with the30 of inlets are neutral with respect to said pulverulent maequilibriumbetween the gas and the water at 650 to terial and wherein thecombustion gases supplied at least 700 C., since through one other setof inlets have oxidizing properties CO with respect to said pulverulentmaterial and wherein the =0.096 combustion gases supplied through atleast one further 2 set of inlets have reducing properties with respectto said and pulverulent material.

H2 3. The process of claim 2, wherein the combustion m=012 gasessupplied through said first set of inlets are neutral with respect tosaid pulverulent material, the combustion gases supplied through thenext set of inlets are oxidizing with respect to said pulverulentmaterial, and the combustion gases supplied through the next two sets ofin- Reduction was efiected by 60 Nrnfi/h. of CO and 46 Nm. /h. ofhydrogen, that is, with heat of reaction input as follows:

mix 50 46 :28 lets are reducing gases with respect to said pulverulent45 material, the latter gases having varying degrees of re- Th h t b l nf th Zone of h f h b r ducing power as between the said last two sets ofinlets. 10, 10a and 10b at an average temperature of the fiuidiza- 4.The process of roasting and fluidizing pulverulent tion bed of 700 C.was as shown in Table VIII. material adapted to be roasted, comprisingforming in a TABLE VIII Input and Inflow Requirements and OutflowIncomplete combustion 0160 kg.lh.heavytuel oil 244 thJh. Available heaof he ore: (9020-0076)X0.22X(700-25) 1, 328 min. Heat of reaction- 2BthJh. Available heat 0! the gases: Available heat of the ore1,141th./l1. Available heat of the preheated air 35 thJh. C0: 00 E10 H;N,

1,443 tl1./h. Nmfl/h 94 10 74 10 315 MtlL/Nmfi 343.40 222.10 265. 56211.85 219.65 125 tlL/h. Sundry... 6 th./h.

1,448 th.lh.

The velocity of the gas when there were no particles single enclosedspace a fluidized substantially horizontal in the bed was flow of saidpulverulent material; introducing combus- 273 1 1 tion gases adapted toroast said material into said fluidized 503 7002-;-3 X =0 50 [IL/sec.flow at a series of stages during the travel of the pulver- 3600 see. 1m1 ulent material in said flow, said gases introduced at said stages,respectively, having dilferent chemical and phy- The gases Onglnatmgfrom an of the burners were sical characteristics with respect to saidpulverulent matrained aft the treatment of the Particles at terial; andremoving the treated pulverulent material at level and did not come anymore 1n contact w1th the the end of i flow fluidized ore. Their sensibleheat was recovered in con- 5, The process f l i 4, h i h proportion ofventio nal manner m a heat ex hangerair in said combustion gases issufficiently changed from Wh1le 'we have furnlshed lllustratlons of theimport stage to stage to change the characteristics with respect andapplicatlon of the invention, these illustratlons do not to saidpulverulent material of the combustion gases supplied at the differentstages between neutral, oxidizing and reducing.

6. The process of claim 4, wherein at the first of said series of stagesin the direction of said fio-w a neutral gas is supplied, wherein at asecond stage an oxidizing gas is supplied and wherein at a third stage arelatively slightly reducing gas is supplied and wherein at a fourthstage a relatively strongly reducing gas is supplied.

7. The process of claim 4, wherein the combustion gas at the first ofsaid series of stages in the direction of said flow includes preheatedair in stoichiometric proportions to provide for a neutral gas, andincludes at the second stage an excess of preheated air so that the gaswhich enters said flow is an oxidizing gas, and wherein the combustiongas of the third stage has a relatively minor deficiency of air so as toprovide a gas having relatively slightly reducing properties, andwherein the combustion gas of the fourth stage is formed with arelatively high deficiency of air so as to provide a strongly reducinggas, the latter deficiency of air being below that which would causecarbon black to form.

8. The process of claim 4, wherein said pul-verulent material is ironore and wherein a combustion gas is supplied at the first of said seriesof stages in the direction of said flow by which said ore is dehydratedbeyond the degree of dehydration accomplished during a preheatingthereof, and wherein a combustion gas is supplied at a second stage inthe direction of said flow by which any carbonates present in the oreare substantially decomposed and any oxides are substantially convertedto sequioxides, and wherein at a third stage in the direction of saidflow a combustion gas is supplied by which a partial reduction of theore to magnetite is accomplished, and wherein at a fourth stage of theflow of the ore the reduction to magnetite is completed.

9. The process of claim 4, comprising forming in a single enclosed spacea fluidized substantially horizontal flow of pulverulent iron ore;moving the particles of said ore in a continuous and substantiallyunimpeded flow in said fluidizing bed from a starting zone to a terminalzone, introducing a combustion gas which is substantially neutral withrespect to said iron ore into said fluidizing bed at a first stage inthe direction of said flow so as to raise the average temperature insaid fluidizing bed to about 250 C., supplying a combustion gas which isoxidizing with respect to said iron ore at a next stage of said flow soas to increase the average temperature of the fluidizing bed to about525 C., supplying a combustion gas which is slightly reducing withrespect to said iron ore at a third stage of said flow so as to increasethe average temperature of said fluidizing bed to about 600 C., andsupplying at a fourth stage of said flow a combustion gas which isstrongly reducing with respect to said iron ore so as to raise theaverage temperature of the fluidizing bed to about 700 C., and removingthe treated ore when it reaches said terminal zone.

References Cited UNITED STATES PATENTS 3,311,466 3/1967 Curlook 262,692,050 10/1954 Nelson 751 2,693,409 11/ 1954 Stephens 75-1 2,711,3686/1955 Lewis 7526 3,105,756 10/ 1 963 Green 75-l 3,189,437 6/1965Boucraut 7526 3,210,180 10/1965 Jukkola 75--1 FOREIGN PATENTS 164,5128/1955 Australia. 1,144,101 4/ 1957 France.

L. DEWAYNE RUTLEDGE, Primary Examiner. E. L. WEISE, Assistant Examiner.

US. Cl. X.R. 7526

